Abstract
This works amid to calculating the absolute efficiency at any interesting.-energy in the energy range between 10 and 1764 keV. by using fit function which has been developed to calculate theoretically the absolute gamma-ray detection efficiencies of a cylindrical NaI(Tl) crystal. Efficiency of the NaI(Tl) calculator is a program built in MATLAB by the author of this paper to make it easier to calculate the efficiency of standard source. The absolute gamma-ray detection efficiencies have been calculated for detectors 3 '' x 3 '' inches NaI(Tl) crystal. The absolute efficiency of the NaI (Tl) detector was calculated using standard sources (IAEA-314) which have known activity of 226Ra (732 Bqkg-1) and 232Th (17.8 ppm). In this calculation, experimental and theoretical efficiencies have been calculated. The uncertainties of efficiency calibration have been calculated also for quality control. Measurements were performed with calibrated point source. Gamma-ray energies under consideration were 0.356, 0.662, 1.17 and 1.33 MeV. Efficiency function was obtained by applying Weibull Model equation to the experimental efficiency data which give Best agreement between experimental and theoretical absolute detection efficiencies of 3x3-inch detector for gamma energy.